This invention relates generally to improvements in pipe joints or pipe couplings of the type having a pair of axially spaced seals to provide a dual seal interface on a matingly interconnected pair of male and female pipe fittings. More particularly, this invention relates to an improved dual seal pipe coupling or joint wherein the inter-seal space is vented at low pressure to prevent seal distortion or damage upon assembly of the pipe fittings in the presence of an incompressible fluid such as water, but further wherein the dual seals provide a substantially leak-free interface in the presence of higher fluid pressure.
Pipe couplings for fluid handling applications are well known in the art, to include a matingly interfitting pair of typically male and female pipe fittings formed on adjacent ends of a pair of conduit members to form an elongated fluid flow path of a desired size and shape. In this regard, elongated conduits or pipes are commonly used in combination with specialized coupling members, such as sleeves, elbows and tees, to provide a custom-configured pipe network to deliver a selected fluid under pressure in gas or liquid form from one location to another. As one example, a typical irrigation system utilizes an array of elongated conduits or pipes assembled with appropriate elbows and tees and the like for delivering irrigation water from a water supply source to a plurality of individual sprinkler devices which distribute the irrigation water to a target terrain area and associated vegetation.
In many irrigation systems, the elongated conduits and associated coupling members are formed from a suitable plastic material for convenient slip-fit and adhesively secured interconnection. While this assembly technique provides a relatively simple leak-free coupling, subsequent rotation of the interconnected pipe components is prohibited. In some instances, such as the connection of a water supply line to an irrigation sprinkler, a so-called swing joint riser assembly is provided with a riser tube and one or more rotatable swing joints to accommodate post-assembly positional adjustment between the interconnected pipe components for orienting the riser tube and associated sprinkler relative to the surrounding terrain. For such swing joint couplings, threaded pipe fittings are typically employed. However, threaded pipe couplings must be tightly interconnected to prevent fluid leakage. Post-assembly rotational adjustment of the riser tube relative to the water supply line typically sets the threadably interconnected pipe components in a partially loosened condition such that some undesirable water leakage can occur.
To resolve leakage problems, swing joint pipe couplings have been developed with one or more seal rings such as resilient O-ring seals to prevent water leakage between the interfitted male and female pipe fittings. In one common design, the male pipe fitting includes a pair of seal rings seated respectively within a corresponding pair of recessed grooves formed at axially opposed ends of an external thread segment. These seal rings are diametrically sized and axially positioned to slidably and sealingly engage annular seal surfaces formed within a threaded bore of the associated female pipe fitting, when the male pipe fitting is threadably assembled therewith. The pair of seal rings provide a dual seal interface to prevent fluid leakage past the interengaged threads, notwithstanding post-assembly relative rotational adjustment between the interconnected male and female pipe fittings.
The dual seal pipe coupling as described above performs well when the pipe fittings are assembled in a dry environment, with fluid in the form of a compressible gas such as air disposed within the inter-seal space between the pair of seal rings. More particularly, as the pipe fittings are assembled, fluid is trapped within the inter-seal space between the axially spaced seal rings. When the trapped fluid comprises a compressible gas such as air, insufficient fluid pressure is generated within the inter-seal space to cause any significant extrusion type distortion or damage to either seal ring. However, when the trapped fluid is an incompressible liquid such as water, a substantial fluid pressure can be generated within the inter-seal space during assembly of the male and female pipe fittings, wherein this fluid pressure can cause undesirable distortion or damage to the seal rings. The presence of an incompressible liquid such as water within the inter-seal space is particularly likely in irrigation system applications since the pipe couplings are often assembled in-the-field in a wet environment.
The present invention provides an improved rotatably adjustable pipe coupling of the dual seal type, wherein fluid trapped within the interseal space at relatively low pressure during assembly of the pipe fittings is vented to prevent seal ring distortion or damage, but further wherein the dual seals provide a substantially leak-tight interface in the presence of higher fluid pressure during normal system operation.